The many different cell types found in blood are all derived from pluripotent hematopoietic stem cells. Stem cells perform two functions: (1) they reproduce themselves, thereby maintaining a stem cell population in the body and (2) they provide progeny cells committed to differentiate into any of the mature blood cell types. The cell which is committed to differentiate along a particular hematopoietic pathway is termed a progenitor cell. Progenitor cells for T lymphocytes, B lymphocytes, granulocytes, macrophages, red blood cells, platelets, and eosinophils, as well as earlier progenitors which can individually give rise to several of the mature cell types, have been studied experimentally both in vivo and in vitro (Dexter, T. M. 1983 J. Pathology 141 415-433). It has been determined in vitro that proliferation and/or differentiation of each progenitor cell type depends upon specific "factors" which have been obtained from various sources. For example, the later progenitors of red blood cells require for their proliferation and differentiation a factor called erythropoietin. The factors required for survival, proliferation and differentiation of the progenitor cells committed to form mature neutrophilic granulocytes and macrophages are called colony stimulating factors (CSFs).
CSF activity has been studied extensively in the mouse. Most adult mouse organs produce CSF activity. However, compositions containing CSF activity that have been obtained from various tissues and by various methods appear to differ in their biochemical characteristics. Thus, the structural relationships between the different factors remain unknown. Furthermore, CSF activity appears to act at more than one step of granulocyte and macrophage development, and again it has been uncertain whether a single factor is responsible for all of the observed activities or whether a different factor acts at each step (Burgess, A. and Metcalf, D. 1980 Blood 56 947-957).
Human CSF activity has been obtained from placenta, certain fetal tissues, macrophages, and stimulated T cells. A line of T cells (Mo) that produces one or more potent CSF activities was established from a patient with a T cell variant of hairy cell leukaemia (leukaemic reticuloendotheliosis) (Golde et al 1978 Blood 52 1068-1072).
The ability of CSF activity to stimulate granulocyte and macrophage production indicates that pharmaceutical compositions having CSF activity are clinically useful in situations where increased production of these (myeloid) cell types is required. Indeed, several patients with extremely high levels of apparently normal circulating granulocytes have been shown to have tumors which over-produce CSFs. In one case, upon surgical removal of the tumor, the granulocyte count rapidly declined towards a normal level, strongly suggesting that CSFs may be useful in regulating the numbers of circulating granulocytes. (Hocking, W., Goodman, J., and Golde, D. Blood 61 600 (1983)). In particular, CSF compositions are useful clinically for the treatment of myelo-suppression caused by chemotherapeutical or irradiation treatment of cancer. In addition, CSF compositions are useful in treating severe infections because CSF can increase and/or activate the number of granulocytes and/or monocytes.
Biological and biochemical characterization of compositions having CSF activity, and study of these compositions in the clinical setting have been hampered to date by the scarcity and impurity of human and/or other primate CSF compositions. It can be appreciated that it would be desirable to identify the protein or proteins responsible for CSF activity. Furthermore, it would be desirable to have a primate, preferably human, source of such CSF activity that could readily supply these proteins in quantities and purity sufficient for biological and biochemical characterization and for use as therapeutic agents.
The Mo cell line has been used both as a starting material for purifying human CSFs and for identifying the corresponding messenger RNAs. However, even with this relatively good source of CSF activity, it has proved to be extremely difficult to isolate protein having sufficient purity for structural studies. Thus, new and better methods for purifying CSFs are desired.